We only know two interstellar visitors, that is, visitors from other stellar systems, in our solar system. They are 1I / ‘Oumuamua and 2I / Borisov. ‘Oumuamua has a lot of press as a strangely shaped traveler that can be from a piece of an exoplanet to an alien ship. The lesser-known 2I / Borisov is more clearly a comet that could have originated near a red dwarf star. His chemical signature suggests that he may never have interacted with a star. If so, said Stefano Bagnulo, of the Armagh Observatory and Planetarium in Northern Ireland, UK:
2I / Borisov could represent the first truly virgin comet ever observed
Bagnulo led a new study on comet 2I / Borisov, published on March 30, 2021 in the peer-reviewed journal Communications on Nature.
He and his team believe that 2I / Borisov had never passed near any star before passing above our sun in 2019. If so, this object could still contain clues about the cloud of gas and dust in which it formed.
Comet 2I / Borisov passed close to our sun in late 2019. In this photo from the Very Large Telescope in northern Chile, the comet is the diffuse object in the center. The stars appear as stripes because the telescope was trained on the moving comet, not the stars. The colors of the stars ’rainbow are the result of combining observations at different wavelengths into a composite image. Image via ESO / O. Hainaut.
A team of scientists led by Bagnulo used a technique called polarimetry to measure 2I / Borisov polarized light. Light is polarized when passing through filters, such as sunglasses or comet material. By studying the properties of sunlight polarized by the dust of a comet, researchers can learn about the physics and chemistry of comets.
This analysis showed that 2I / Borisov was different from almost all other comets studied except Hale-Bopp. Astronomers believe that comet Hale-Bopp only passed through the sun once before its magnificent return in the late 1990s. This earlier return is believed to have occurred thousands of years ago, in 2215 BC, when Hale-Bopp may have had almost a collision with Jupiter, altering its orbit and bringing it to the sun for the first time. Due to its few interactions with the sun, Hale-Bopp is also considered a virgin comet, with a composition very similar to that of the cloud of gas and dust that formed our solar system 4.5 billion years ago.
Polarization data show that 2I / Borisov is even more virgin than Hale-Bopp. 2I / Borisov shows unmarked signatures of the gas and dust cloud of its formation. Evidence also shows that both comets formed under similar conditions, only in different solar systems. As Alberto Cellino of the Turin Astrophysics Observatory said:
The fact that the two comets are remarkably similar suggests that the environment in which 2I / Borisov originated is not so different in composition from the initial solar system environment.
Comet Hale-Bopp, seen here on April 4, 1997, was another of the most virgin comets known, meaning that it has had few interactions with its star, in this case our sun. Comet 2I / Borisov is also virgin, with its hovering near the sun in 2019 which is believed to be its first interaction with any star. Image via E. Kolmhofer / H. Raab / Johannes-Kepler-Observatory / Wikimedia.
A second team of scientists used telescopic data to analyze 2I / Borisov dust grains and published their findings on March 30, 2021 in the peer-reviewed journal Nature Astronomy.
They discovered that the comet’s coma, which is the dust envelope that surrounds the main body of a comet, contains compact pebbles. These pebbles are about 1 millimeter (0.04 inches) large. The team also noted that the comet’s relative amounts of carbon monoxide and water changed drastically as it approached the sun. According to these scientists, these changes indicate:
… that the comet is made up of materials that formed in different places in its planetary system.
The observations of [Bin Yang, an astronomer at ESO in Chile] and his team suggest that the matter in 2I / Borisov’s planetary home was mixed from near the star to beyond, perhaps due to the existence of giant planets, the strong gravity of which shakes material in the system. .
Astronomers believe that a similar process occurred early in the life of our solar system.
When amateur astronomer Gennady Borisov discovered comet 2I / Borisov in August 2019, it became the only known object to visit our solar system from interstellar space. The first discovery was ‘Oumuamua in October 2017.’ Oumuamua was moving at a speed of 94,800 km per hour until its oscillation beyond the sun accelerated it to 315,800 km per hour.
These zippy interstellar visitors are already leaving the solar system and returning on their way to interstellar space.
This diagram compares the paths of the two known interstellar objects that have entered our solar system, 1I / ‘Oumuamua (red, discovered in 2017) and 2I / Borisov (yellow, discovered in 2019). Image via Wikimedia / Tony873004.
Abstract: The second known interstellar object, called comet 2I / Borisov by terrestrial astronomers, may be one of the most virgin objects ever seen, according to a new study.
Source: Unusual polarimetric properties for the interstellar comet 2I / Borisov
Source: compact pebbles and evolution of volatiles in the interstellar comet 2I / Borisov
Via ESO
